There are infections out there, however, that are often fatal and can’t be treated with antibiotics. These are usually viral in nature. Last time, we talked about HIV, hemorrhagic fevers like Ebola and its relatives, plus the rodent-borne Hantavirus.

In this part of our series on deadly viruses, we’ll go over a few well-known diseases, but also cover some that you may not have heard about.

ROTAVIRUS

Dehydration from intestinal viruses is a major killer in less-developed countries

The World Health Organization reports that this virus kills more than half a million children annually worldwide. They even believe that every child on the planet has been infected at least once with it. You get it by ingesting bad food and water or touching surfaces contaminated with infected feces.

Once in the body, rotavirus infects the cells that line the gut. It emits a toxin which causes symptoms in two or three days that can last a week or more. They include severe watery diarrhea, fever, vomiting, and abdominal pain cramps. Coupled with a loss of appetite, children rapidly go into a state of dehydration. If fluids are not replaced quickly, they may succumb to the illness. This is the most common cause of death in less developed areas.

Although a vaccine exists for rotavirus, even vaccinated children may get sick multiple times. Future infections, however, tend to be milder. The virus is rarely lethal to adults.

Symptoms of dehydration, especially in children and infants, may be hard to discern, but they include:

decreased volume of urine, usually darker than normal

dry mouth

feeling dizzy when upright

skin that tents up when stretched

crying with few or no tears and

unusual sleepiness or fussiness

RABIES

Dog with Rabies

Much more well-known than rotavirus is Rabies, a virus transmitted when an infected animal scratches or bites another animal or human. Saliva from an infected animal has a heavy viral load which can also spread infection if it splatters into the eyes, mouth, or nose of someone nearby.

Globally, dogs are the most common animal involved, accounting for more than 99% of rabies in many countries. In the Americas, however, you might be surprised to known that bat bites are the most common source of rabies infections in humans (less than 5% of cases are from dogs). Rodents are often blamed, but they’re very rarely infected with rabies. Interestingly, birds given the rabies virus via injection seem to experience no illness whatsoever.

Rabies caused more than 17,000 deaths worldwide in 2015, mostly in Africa and Asia. The period between infection and the first symptoms (the “incubation period”) is typically 1–3 months in humans, but can be much longer. This, along with a death rate of almost 100 per cent if untreated, is the reason why humans suspected of being exposed are given a series of vaccinations and antibodies as soon as possible.

Symptoms usually begin as fever and headache, but the illness progresses to affect the nervous system, causing paralysis in many cases. Rabies causes significant alterations in mental status, including confusion, agitation, anxiety, paranoia, hallucinations, and general delirium.

One unusual sign of rabies is hydrophobia, the fear of water. Because of difficulty swallowing despite severe thirst, water seems to panic victims. It’s at this point that patient produce a large amount of saliva, making them appear to “foam at the mouth”. Death usually occurs within a few days after symptoms appear.

There are a couple of different forms of rabies. Hydrophobia is commonly associated with what they call “furious” rabies (80% of those infected). The remaining 20% mostly exhibit signs of paralysis (“paralytic” rabies) and numbness; this form doesn’t cause hydrophobia.

SMALLPOX

British gave “gifts” of blankets from the smallpox ward to Native Americans in colonial times

In 1980, the World Health Assembly declared the world free of smallpox. You may wonder why, then, I would list smallpox in this article. Simply put, there are a lot of diseases that aren’t common now that will become common if we are thrown off the grid due to some major disaster. It pays to know how to identify them.

Before its theoretical “eradication”, humans battled smallpox for thousands of years, and the disease killed one in three of those infected. Survivors were left with permanent scars and, sometimes, blindness. Smallpox could be transmitted through the air or by contact with victims or contaminated items.

Mortality rates were far higher outside of Europe, where smallpox was endemic. People elsewhere had little contact with the virus and so had no natural immunity to it. Historical accounts estimate that 90 percent of the native population in some areas of the Americas died from smallpox introduced by European explorers. Smallpox killed 300 million people just in the last century.

After an incubation period of 7 to 17 days, a series of flu-like symptoms appear suddenly. You’ll see:

Fever

Headache

Fatigue

Aches and pains

Severe back pain

Vomiting

As time progresses, a wave of flat red spots appears on the face, arms, and legs, spreading to the torso and elsewhere (even the oral cavity) over time. Many become small blisters which fill with pus and scab over, falling off a week or so later. Deep, pitted scars were often seen in patients that recovered from the illness.

Chickenpox vs Smallpox

WebMD describes the difference in appearance between the sores in Smallpox vs Chickenpox as follows:

“Chickenpox sores show up at different times in different areas. They’re mostly on the stomach, chest, and back, and rarely on the palms or the soles of your feet.

Smallpox sores appeared all over the body at the same time (mostly on the face, arms, and legs, and sometimes on the palms and soles) and all looked the same.”

DENGUE VIRUS

Dengue virus is a pathogen (disease-causing organism) spread by mosquito bites. It first appeared in Asia but has spread to every tropical or subtropical part of the planet. Dengue causes mild illness in tens of millions every year; in the worst cases, however, a hemorrhagic fever develops which has a 20% death rate.

Once bitten by an infected mosquito, people will begin to feel sick four to seven days later. You will likely see:

High fever

Headache

Pain in muscles and joints

Nausea and vomiting

Swollen glands

Rash

Luckily, most victims will recover completely within a week. In severe cases, the circulatory system become damage and blood-clotting factors are depleted. These unlucky patients will present with:

Worsening abdominal pain with vomiting

Spontaneous bleeding under the skin (bruises) and from the nose or gums

Blood in the urine, vomit, or bowel movements

Difficulty breathing

Dengue virus is related to the Zika Virus, which affected the brain development of fetuses in pregnant women bitten by infected mosquitoes.

YELLOW FEVER

Yellow Fever is a virus related to both Zika and Dengue. In most cases, it produces no symptoms at all. In a minority, however, symptoms very similar to those listed above for Dengue virus occur. Most will recover fully in a week or so.

In perhaps one in seven, however, a more severe form of the disease occurs which affect the liver and other organs. These victims feel better for a short time before relapsing. You will see:

The return of high fever

Yellowing of the skin and eyes

Spontaneous bleeding as in Dengue

Shock

Organ failure

You may think there isn’t a deadlier set of viruses than what we’ve described so far in this series, but there is: It’s called influenza. More on the flu next time.